1. Field of the Invention
The present invention relates to a sheet stacking apparatus having a function of aligning a sheet on a stacking tray.
2. Description of the Related Art
Conventionally, there has been a system, in which a sheet post-processing apparatus is connected to an image forming apparatus downstream thereof in a sheet conveyance direction, for performing post-processing such as staking processing, stapling processing, and punching processing.
In the above-described system, a sheet, on which an image is formed by the image forming apparatus, is conveyed and stacked onto a sheet discharge tray in the sheet post-processing apparatus. A user may perform post-processing on the sheet stacked on the sheet discharge tray using an offline apparatus, or may directly pack the sheet as a product in a box. Therefore, the sheet post-processing apparatus that stacks the sheet onto the sheet discharge tray has required high-precision alignment and sorting properties.
In response to the above-described request, Japanese Patent Application Laid-Open No. 2006-206331 discusses a configuration in which an alignment member is provided on a sheet discharge tray in an apparatus capable of sorting and stacking (hereinafter referred to as shift stacking) a sheet, and the alignment member abuts on an edge of the sheet parallel to a sheet discharge direction to align a position of the edge of the sheet, and stacks the sheet.
Conventionally, a user selects whether a plurality of sheet bundles formed by an image forming system is shift stacked or non-shift stacked according to how the sheet bundles will be processed later.
However, in the configuration discussed in Japanese Patent Application Laid-Open No. 2006-206331 and when shift stacking is not selected, the following issue occurs in an apparatus having a configuration in which a sheet is stacked at the center of a stacking tray. As illustrated in FIG. 11, when a sheet, which is not designated to be shift stacked, is newly stacked and aligned with sheet bundles shift stacked on a sheet discharge tray, an alignment plate 711a or 711b, which contacts the sheet moves to rub already stacked sheets. As a result, the already stacked sheets, which have been shift stacked, may be damaged by scratches or dirt.